Quaternary ammonium compounds (quats) are typically prepared by the reaction: EQU R.sup.1 R.sup.2 R.sup.3 N+R.sup.4 X.fwdarw.R.sup.1 R.sup.2 R.sup.3 R.sup.4 NX (I)
wherein X is a halogen, a sulfate, a sulfo compound, or the like. When at least one of R.sup.1, R.sup.2, R.sup.3, or R.sup.4 is C.sub.12 or longer, the product is an inert soap. Many of the inert soaps have biocidal activity against bacteria, fungi, algae, and related organisms.
Reaction (I) above is limited by the reactant R.sup.4 X because R.sup.4 must react with tertiary amines. For example, methyl chloride (R.sup.4 X.dbd.CH.sub.3 Cl) will react with a tertiary amine at less than 100.degree. C. to yield a quaternary compound R.sub.3 N.sup.+ CH.sub.3 Cl.sup.-, while methanol or methyl acetate (R.sup.4 X.dbd.CH.sub.3 OH or CH.sub.3 COOCH.sub.3) will not, under similar reaction conditions.
General quaternary ammonium compounds with a sulfo group are easily prepared either by the reaction of a sulfate compound with a tertiary amine (II) or by a double exchange (III). EQU R.sub.3 N+RSO.sub.3 CH.sub.3 .fwdarw.R.sub.3 NCH.sub.3.sup.+ RSO.sub.3.sup.-(II) EQU R.sub.3 N.sup.+ CH.sub.3 Cl.sup.- +RSO.sub.3.sup.- Na.sup.+ .fwdarw.R.sub.3 NCH.sub.3.sup.+ RSO.sub.3.sup.- +NaCl (III)
Quaternary ammonium hydroxides (hydroxy quats) are currently prepared by the reaction of quaternary ammonium iodide with silver oxide (IV). EQU RN.sup.+ (CH.sub.3).sub.3 I.sup.- +AgO.fwdarw.RN.sup.+ (CH.sub.3).sub.3 OH.sup.- +AgI (IV)
However, this reaction is costly, and it is difficult to recover the silver reagent. See, Organic Reactions, 11:Chptr 5, pp. 376-377, Krieger Publishing Co., 1975.
In an olefin synthesis, it has been suggested to treat a quaternary salt with aqueous sodium or potassium hydroxide followed by pyrolysis in order to form the hydroxy quat and then to decompose the hydroxy quat directly. However, in this method the hydroxy quat is not isolated and the conditions for its preparation are undesirable. See, Organic Reactions, 11:Chptr 5, pp. 376-377, Krieger Publishing Co., 1975.
Talmon et al., Science, 221, 1047 (1983), have used an ion exchange resin to convert didecyldimethylammonium bromide to didecyldimethylammonium hydroxide (V). EQU (C.sub.12 H.sub.25).sub.2 (CH.sub.3).sub.2 N.sup.+ Br.sup.- +Ion Exchange Resin.fwdarw.(C.sub.12 H.sub.25).sub.2 (CH.sub.3).sub.2 N.sup.+ OH.sup.-(V)
However, 50 ml of ion exchange resin and two treatment steps were required to convert 3 grams of quaternary ammonium chloride to the corresponding hydroxide. See also, Organic Synthesis, Collective Volume VI, 552, John Wiley Inc., 1988; Brady et al. J. Am. Chem. Soc., 106:4280-4282, 1984; Brady et al. J. Phys. Chem., 90:9, 1853-1859, 1986; Miller et al. J. Phys. Chem, 91:1, 323-325, 1989; Radlinske et al. Colloids and Surfaces, 46:213-230, 1990.
Alternatively, quaternary ammonium hydroxide compositions have been prepared by treating a haloquat in an electrochemical cell with special cation exchange diaphragms between the cells. The hydroxy quat collects at one electrode, and the halide collects at the other. See, Japanese Patent Publication No. 02-106,915; Awata et al., Chemistry, Letters, 371 (1985).
Japanese Patent Publication No. 01-172,363 discloses the preparation of relatively low yields of tetraethylammonium hydroxide by reacting triethylamine with diethyl sulfate, heating the resultant quat with sulfuric acid to yield the sulfate quat, and reacting the sulfate quat with barium hydroxide to yield the short chain quat, tetraethylammonium hydroxide, and barium sulfate.
Di C.sub.8 -C.sub.12 alkyl quaternary ammonium hydroxides prepared by ion exchange were used as strong bases to digest animal tissue by Bush et al., French Patent Publication No. 1,518,427.
Akzo discloses that the addition of a metallic hydroxide to a quaternary ammonium chloride such as didecyldimethylammonium chloride, in an aqueous medium, results in an equilibrium mixture of quaternary ammonium chloride and quaternary ammonium hydroxide (VI). This reaction can be driven to the right by the use of isopropanol as a solvent. EQU (R.sub.4 N)Cl+KOH.revreaction.(R.sub.4 N)OH+KCl (VI)
Quaternary ammonium compounds (quats) and particularly didecyldimethylammonium chloride (DDAC) ##STR1## could be used as wood preservatives if they were stable because they possess resistance properties to fungi and termites, to loss of strength, and to electrical sensitivity similar to those of commonly used acidic copper/chromium/arsenic solution (CCA) or ammoniacal copper and arsenic salt solution preservatives. See Proc of the Am. Wood Pres. Assoc., 80:191-210 (1984). Although chloride quats do not include potentially dangerous heavy metals, didecyldimethylammonium chloride leaches rapidly in soil (Nicholas et al., Forest Prod. J., 41:41 (1991), and therefore, does require coupling with copper salt.
Findlay et al., U.S. Pat. No. 4,929,454, disclose a method of preserving wood by impregnation with a quaternary ammonium compound and at least one of zinc and copper, wherein the quat anion is chosen from the group consisting of hydroxide, chloride, bromide, nitrate, bisulfate, acetate, bicarbonate, and carbonate, formate, borate and fatty acids. These quats have distinct environmental and safety advantages over commonly used acidic copper/chromium/arsenic solution (CCA) or ammoniacal copper and arsenic salt solution preservatives in that potentially dangerous heavy metals are not included. The Findlay et al. quats require copper or zinc in order to render them relatively insoluble and to prevent them from leaching out of a treated substrate. The use of copper or zinc in the above formulations may yet raise environmental and corrosion concerns.
Additionally, didecyldimethylammonium chloride tends to absorb preferentially to the surface of the wood and does not uniformly treat the whole substrate. Finally, DDAC treated wood shows surface erosion or ages upon exposure to light. See Preston et al., Proc. Am. Wood Pres. Assoc., 83:331 (1987).
The biocidal activities of various chloride quats against bacteria, fungi, and algae are tabulated in Cationic Surfactants, E. Jungerman Ed., pp. 56-57, Marcel Dekker, Inc., 1969. Nicholas, "Interaction of Preservatives with Wood," Chemistry of Solid Wood, Advance in Chemistry Series #207, Powell ed., (A.C.S. 1984) notes that didecyldimethylammonium compounds and particularly DDAC are potential biocides. Preston, J.A.O.C.S. 60:567 (1983) concurs and suggests that maximum fungitoxicity is exhibited with dialkyldimethyl compounds having C.sub.10 -C.sub.12 alkyl groups. Butcher et al., Chem Abstracts No. 91:152627b, suggests that the presence of an acid or a base can affect the activity of didecyldimethylammonium quats.
Consequently, efforts have been directed to develop a safe, efficient and expedient method to prepare quaternary ammonium compounds that do not require potentially hazardous metal additives to treat wooden substrates effectively.